In many sports shoes, running shoes and the like, shock absorbing members (shock absorbing structures) are incorporated in order to absorb impacts which are applied to legs (feet, knees and the like) of those who wear the shoes. A number of research and development activities have been earnestly carried out, and various proposals have been made as such shock absorbing structures.
As shock absorbing materials having excellent shock absorbing performance as described above, structures adopting gels and rubbers (soft materials) with low hardness are known (refer to Patent Literatures 1 to 10, for example).
Since it is important to design the structure that can absorb impact to the greatest extent possible with respect to extremely large impact at a time of running and at a time of jumping, these soft materials are especially provided directly under and in vicinities of regions directly under heels, thenars and hypothenars, and therefore, most of the soft materials have been hidden inside shoe soles (or inside the soles) in general. There has been a room for improvement in the point that although the materials themselves have high shock absorbing performance, the states of the soft materials cannot be confirmed from outside, and therefore, one of the problems has been to increase the ability to attract attention as a product.
Further, there also has been the problem that the performance of the soft material cannot be sufficiently exhibited since after the soft material is sealed inside the shoe sole, a space for the soft material to deform sufficiently cannot be ensured, and the performance of the soft material is influenced by the performance of the shoe sole material.
Further, in order to enhance the shock absorbing characteristic, it is effective to increase the deformation amount of the soft material, but since deformation in the compression direction has been mainly adopted conventionally, the deformation amount has been limited in the limited thickness condition, so that there has been inevitably a limitation on improvement of the shock absorbing performance. As the shock absorbing member which practically performs a shock absorbing action is made softer, the shock absorbing characteristic is enhanced more, but when the shock absorbing member is too soft, the shock absorbing member is compressed completely at a time of pressure reception, so that bottoming occurs, or even when bottoming does not occur, a repulsion characteristic is so small that in the process from landing to kicking-out with a tiptoe, a so-called repulsion characteristic is reduced, such as excessive turning of an ankle and a deviation of the center of gravity (landing stability), and reduction in a propulsion force by a repulsive force at the time of kicking out, and therefore, there has been the problem to make a shock absorbing characteristic and performance of facilitating running and jumping compatible. Further, in the case of a viscoelastic material such as gels and rubbers, there has been generally the problem that bonding to other members is relatively difficult as the softness of the material is increased.
For the above reason, the shock absorbing structure and shoes have been pursued, which can expose a soft material to outside, in particular, expose most of the outer peripheral face to outside to the maximum extent so that presence of the soft material can attract attention of users as much as possible, and can keep performance of facilitating running and jumping while exhibiting high shock absorbing performance, at the same time. Further, there has been an increasing need for customizing shock absorbing performance on site in accordance with the feet conditions over time of a wearer (change in a running characteristic and a walking characteristic following foot podedema and fatigue).
Meanwhile, as the prior art of the structure in which a shock absorbing material is exposed to outside, there is proposed a shoe in which a column-shaped (columnar) shock absorbing material is fixedly disposed in a sole, and a periphery of the shock absorbing material is opened (refer to Patent Literature 11, for example).
However, it is not sufficient to simply expose a shock absorbing material to outside. That is, when a columnar shock absorbing material is vertically fixed between a midsole and an outer sole as in Patent Literature 11 described above, the shock absorbing material easily causes “unsteadiness” as the column bends and tilts by compression deformation, and therefore, use of a rigid resin material for the columnar member, or another support member for a periphery are required. In this way, a shock absorbing characteristic against impact in the vertical direction can be ensured more or less, but shock absorbing characteristics against a number of impacts and deformations from diagonal directions, which occur in actual use are lost.
If the columnar shock absorbing member is made of a softer material, the shock absorbing material (soft material) which is fixed between the midsole and the outer sole has deformation restricted (arrested) by the upper and lower junction faces, and therefore, there is no change in the fact that high shock absorbing performance itself which is peculiar to a soft material is significantly restricted (in particular, at a time of start of deformation).
Further, although there is proposed a shoe which is enhanced in shock absorbing performance by increasing the deformation amount by causing the soft material to undergo shearing deformation in the diagonal direction in addition to compression deformation (refer to Patent Literature 4, for example), almost no attention has been paid to bulging deformation of the soft material.